Homopolymers and copolymers of 4-hydroxystyrene, a compound which is also known as p-vinylphenol, are well known compositions which are used in the manufacturing of metal treatment compositions, photoresists, epoxy resins and epoxy resin curing agents. Polymers of 4-hydroxystyrene can be produced by polymerizing the 4-hydroxystyrene monomer. That monomer, however, is an unstable compound under room temperature and must be stored under low temperatures provided by refrigeration to prevent its spontaneous polymerization. Even under low temperatures, the monomer slowly polymerizes to low molecular weight polymers.
Because of the instability of the 4-hydroxystyrene monomer, alternative routes for preparing polymers of 4-hydroxystyrene have been utilized using 4-acetoxystyrene, the acetic acid ester of 4-hydroxystyrene, as the starting compound. 4-Acetoxystyrene is a stable monomer which can be readily polymerized and copolymerized to low, medium and high molecular weight polymers. Those processes involve the polymerization of the 4-acetoxystyrene monomer, followed by the hydrolysis of the phenolic ester groups of the 4-acetoxystyrene polymers to produce 4-hydroxystyrene polymers.
Corson et al., Preparation of Vinylphenols and Isopropenylphenols, 23 J. Org. Chem. 544-549 (1958) (hereinafter referred to as "Corson, et al."), discloses a process for making 4-hydroxystyrene from phenol. According to that process, phenol is acylated to 4-hydroxyacetophenone which is then acetylated to 4 -acetoxyacetophenone. The latter compound is hydrogenated to 4-acetoxyphenylmethylcarbinol which is, then, dehydrated to 4-acetoxystyrene. The 4-acetoxystyrene is saponified to 4-hydroxystyrene using potassium hydroxide.
Packham, Chelating Polymers Derived from Poly-4-Hydroxystyrene, 1964 J. of the Chemical Society 2617-2624, describes the hydrolysis of cross-linked poly (4-hydroxystyrene) by refluxing the polymer in alkaline aqueous dioxan. Arshady, et al., Phenolic Resins for Solid-Phase Peptide Synthesis: Copolymerization of Styrene and p-Acetoxystyrene, 12 J. of Polymer Science 2017-2025 (1974), describes the hydrolysis of copolymers of styrene and p-acetoxystyrene to the vinylphenol polymer using hydrazine hydrate in dioxane.
Chen, et al., A Morphological Analogue of Japanese Lacquer. Grafting of p-Hydroxystyrene onto Pullulan by Ammonium Persulfate Initiation in Dimethylsulfoxide, 23 J. Polymer Science: Polymer Chem. Ed. 1283-1291 (1985) describes the hydrolysis of p-acetoxystyrene grafted pullulan to p-hydroxystyrene pullulan with hydrazine hydrate. Nakamura, et al, Effect of Substituent Groups on Hydrogen Bonding of Polyhydroxystyrene Derivatives, 15 Polymer J. 361-366 (1983), describes the hydrolysis of poly(p-acetoxystyrene) dissolved in acetone to poly(p-hydroxystyrene) with hydrochloric acid.
U.S. Pat. No. 2,276,138 discloses the ester interchange reaction of poly (4-acetoxystyrene) in methanol using sodium methylate. About 84 percent of the acetate groups are removed by the interchange reaction.
U.S. Pat. No. 3,547,858 discloses a process for the production of polymers containing hydroxyl groups which comprises subjecting a polymer of an ester of an unsaturated alcohol to the action of a hydrolyzing agent while the polymer is in the molten state. In the hydrolysis reaction, the ester groups are replaced by hydroxyl groups. Water and, preferably, a lower alkyl alcohol can be used as a hydrolyzing agent.
U.S. Pat. No. 4,544,704 discloses the hydrolysis of a copolymer of styrene and p-isopropenylphenylacetate with aqueous sodium hydroxide in methanol and toluene using a small amount of benzyltrimethylammonium chloride as a phase transfer agent.
U.S. Pat. No. 4,678,843 discloses a process for hydrolyzing polymers of 4-acetoxystyrene to polymers of p-vinylphenol, and which process is conducted entirely in solution. Ammonia is the hydrolysis catalyst. The 4-acetoxystyrene polymer is dissolved in a solvent which is miscible with water. Ammonia gas or ammonium hydroxide is added to the solution and the hydrolysis reaction is carried out at a temperature of about 50.degree. C. to about 150.degree. C. for a time sufficient to hydrolyze the acetoxy groups to phenol groups. At the end of the hydrolysis reaction, wet carbon dioxide gas is introduced into the reaction solution as a sparge below the solution surface to remove the ammonium salt. The 4-hydroxystyrene polymer is recovered for use as an organic solvent solution and can be recovered as a solid by removal of all solvents by vacuum distillation or by precipitating the polymer from the solution.
U.S. Pat. No. 4,689,371 discloses the production of poly-(4-vinylphenol) by hydrolyzing polymers of 4-acetoxystyrene by methanolysis with quaternary ammonium hydroxides as the catalyst. The 4-acetoxystyrene polymer is dissolved in a solvent which is miscible with water. Ammonium hydroxide is added and the reaction is carried out at a temperature of about 50.degree. C. to about 80.degree. C. for a time sufficient to hydrolyze the acetoxy group. The reaction product is heated to a temperature of about 50.degree. C. to about 150.degree. C. to distill off methyl acetate and the decomposition products of the quaternary ammonium hydroxide. The 4-vinylphenol polymer can be used per se as a solution or it can be recovered as a solid by removal of all solvents by vacuum distillation or by precipitating the polymer from the solution.
U.S. Pat. No. 4,822,862 discloses the production of homopolymers and copolymers of p-vinylphenol by hydrolyzing homopolymers or copolymers of 4-acetoxystyrene with a base such as an alkali metal hydroxide, an ammonium hydroxide, a quaternary ammonium hydroxide or a water soluble amine. The hydrolysis reaction occurs in an emulsion containing the polymers of 4-acetoxystyrene in water, without isolating the polymer. The vinylphenol polymer is recovered from the emulsion by acidifying the reaction mass and by filtering, washing and drying the solid polymer or by coagulating the emulsion with alum and, after acidification, recovering, washing and drying the solid polymer.
U.S. Pat. No. 4,857,601 discloses the selective hydrolysis of copolymers of p-acetoxystyrene and dialkyl muconates or alkyl sorbates to copolymers of p-vinylphenol and dialkyl muconates or alkyl sorbates using acid or base catalysts in an alcohol or water. The reactant copolymer is slurried in an alcohol or aqueous base. The product is dissolved in the alcohol or aqueous base and is recovered as a solution.
U.S. Pat. No. 4,868,256 discloses the hydrolysis of polymers of 3,5-dibromo-4-acetoxystyrene to polymers of 3,5-dibromo-4-acetoxystyrene with a base or an acid such as tetramethyl ammonium hydroxide, aqueous NH.sub.3, NaOH, KOH, HCl, and H.sub.2 SO.sub.4.
U.S. Pat. No. 4,877,843 discloses the selective hydrolysis of copolymers of 4-acetoxystyrene and allyl esters of unsaturated acids slurried in an alcohol or water to copolymers of p-vinylphenol and allyl esters of unsaturated acids with an acid or a base. If the reaction is an alcoholysis reaction in alcohol, the polymer can be recovered by precipitating and coagulating the polymer in water. If the hydrolysis reaction is carried out in aqueous base, the polymer can be recovered from solution by precipitation with acid. The alcohols used are the one to four carbon alcohols. The acids used are mineral acids and organic acids with dissociation constants in aqueous solution of less than 2. The bases used are alkali metal hydroxides and alkoxides and quaternary ammonium hydroxides. The processes of this patent are conducted entirely in solution.
U.S. Pat. No. 4,898,916 discloses the production of polymers of 4-vinylphenol by the acid catalyzed transesterification of polymers of 4-acetoxystyrene in an alcohol. Polymers of 4-acetoxystyrene are slurried in an alcohol and are hydrolyzed to polymers of 4-vinylphenol in the presence of a mineral or organic acid as well as Lewis acids which have dissociation constants in aqueous solution of less than 2. The alcohols used are one to four carbon alcohols. The 4-vinylphenol polymer product is recovered as a solution in the alcohol to be used as such or it can be further recovered as a solid from such solutions by utilizing well known techniques.
U.S. Pat. No. 4,912,173 describes the hydrolysis of homopolymers of 4-acetoxystyrene suspended in water in finely divided particulate form to homopolymers of 4-hydroxystyrene using aqueous nitrogen bases. The nitrogen bases used are ammonia, primary, secondary or tertiary water soluble amines and water soluble quaternary ammonium hydroxides. When ammonium hydroxide is used as the base, the suspended polymer product remains in suspension and the water is removed by filtration, decantation or centrifugation. After washing and drying the polymer is ready for use. When other bases are used, the particles are sometimes softened or solubilized. Agglomerated polymers can be recovered by removing the water, washing and drying, as described above. Solubilized polymers are recovered after precipitation with acid. This patent only discloses processes for homopolymers.
U.S. Pat. No. 4,962,147 discloses the hydrolysis of poly(4-acetoxystyrene), in suspension in its polymerization medium, to poly(4-hydroxystyrene) with ammonia. Ammonia is preferably used as ammonium hydroxide. It can also be used in gaseous form which is preferably introduced below the surface of the aqueous reaction medium. During the hydrolysis reaction, the suspended homopolymer remains in suspension in solid finely divided form.
U.S. Pat. No. 4,965,400 discloses the hydrolysis of 3,5-disubstituted-4-acetoxystyrene to form substituted 4-hydroxystyrene analogs. The hydrolysis agents are NH.sub.3, NaOH, KOH, tetramethylammonium hydroxide, HCl or H.sub.2 SO.sub.4.
In most of the above referenced processes, the reaction was carried out with the reactants being in solution or the 4-hydroxystyrene polymer product was recovered as a solution. As a result, a large reactor volume was required to accommodate the reaction. Furthermore, in order to recover the product as a solid from the solution, certain steps had to be used such as precipitation with a non-solvent, acidification of the salt form of the polymer, spray drying or the like. Such steps were time-consuming and uneconomical because they required additives and/or energy. In each case, copolymers could not be hydrolyzed without being totally dissolved before or during hydrolysis.
According to the present invention, the hydrolysis reaction is carried out only in suspension and the copolymer product thereof is in suspension. The solid product is intact and is easily and economically recovered by well known techniques such as filtration.
Another disadvantage of prior processes was that, oftentimes, a satisfactory degree of hydrolysis of copolymers of 4-acetoxystyrene to copolymers of 4-hydroxystyrene could not be achieved when the amount of 4-acetoxystyrene in the reactant polymer was less than about fifty (50) weight percent of the total weight attributed to 4-acetoxystyrene and the copolymer polymerizable therewith. According to the present invention, copolymers of 4-acetoxystyrene are hydrolyzed to a satisfactory degree with hydroxylamine regardless of the amount of 4-acetoxystyrene present therein.
These and other advantages of the present invention will become apparent from the following description.